The last stage in producing a cask conditioned beer is the addition of a fining agent to clarify the beer. The most commonly used is Isinglass. This was traditionally produced from the swim bladder of the sturgeon. It is of course one of the great mysteries of the universe, how anybody discovered that fish bits will clear beer. There appears to be an electrostatic attraction between the yeast cells and the collagen in the isinglass. This causes the particles to flocculate and these large masses then sink to the bottom of the cask.
Usually 24 hours will be allowed for this to happen before tapping, but many beers will clear much faster than this.
Over use of isinglass can result in threads of the isinglass rising from the base of the cask and being drawn out of the tap. This will produce a murky pint and is known as “fluffy bottoms”
It has been known for a long time that isinglass is very effective at clearing beer and wine.
Before effective distillation methods were developed it was used in Russia to clear vodka.
This record from 1568 shows big imports of the stuff into Britain.
Charitie of London (100) Thomas Awdley; Russia
John Brook ‘et sociis’: 170 cwt wax, 750 cwt cordage, 80 lbs raw silk, 100 calf skins ‘in the hair’, 10 lasts tar, 400 lbs cinnamon, 100 lbs mace, 10 cwt yarn, 3 hd lbs isinglass, sealskins ad valorem £2, 40 wolfskins, 60 wolverines cost £2 a piece, 10 timber minks, 100 ermines, 100 beaver bellies, 5 beaver backs, 20 lbs rhubarb £1 314
In the 1660’s Vintners had to be licensed to Charles II and pay duty on imports of isinglass
Richard Hutton’s complaints book 0f 1725 p162 gives a good description of the process.
To fine a 30 gallon cask of strong beer or ale.
“Take about 2 ounces of the finest & clearest isinglass beat or cut very small, put it into an earthen vessel with as much vinegar (or alligar) as will cover the isinglass. Brush it very well with a whisk twice or thrice a day till it be quite dissolved & as it grows thick put a little more vinegar to it till it becomes a very thick syrup, then strain through a cloth about a pint thereof (or more if over thin), then open the bung of the cask. With a whisk then pour in the strained isinglass, stirring it very well also & bung the cask very close & in 24 hours your drink will be very clear . . . So in proportion may fine any greater or less quantity, but be sure when you put those things into the drink that you make everything so close as that you cannot draw any at the tap without first making a vent at top, lest your drink grow flat.”
In 1795 William Murdoch developed a replacement for isinglass. Murdoch’s replacement was made from dried Cod and was much cheaper than the 25 shillings a pound which isinglass cost. This cost saving was so attractive that the Committee of London Brewers paid £2000 for the right to use his invention.
Murdoch’s isinglass replacement was so effective that in a court case brought by the British Customs and Excise Authorities, the noted Chemist, Sir Humphry Davy in answer to a question on whether it was “proper to be used for the purpose of fineing beer” testified that:
I believe it is if properly prepared – it is the same substance as Isinglass.
Use of Murdoch’s “Isinglass made of British fish” continued and played an important role in reducing British brewers reliance on imported raw materials.
Although alternatives are available, isinglass is still very widely used in the brewing industry.